1. Field of the Invention
The present invention relates to a carriage shifting apparatus wherein a carriage is shifted by transmitting a driving force to the carriage via pulleys and a belt or rope, and a serial recording system utilizing such carriage shifting apparatus.
2. Related Background Art
In the past, as systems which are operated by reciprocally shifting a carriage, serial recording systems and original (document) readers of serial type are well known. For example, in such serial recording systems, as shown in FIG. 7, a recording head 51 is mounted on a carriage 50 and an image such as a character is recorded on a recording medium 52 by serially scanning the carriage 50. Further, in the conventional serial original readers, an image sensor (in place of the recording head 51) is mounted on the carriage 50 and an image is read by serially scanning the carriage 50. Conventionally, in order to serially scan the carriage 50, generally, the carriage 50 is connected to an endless timing belt 56 extending between and mounted around a driving pulley 54 connected to a motor 53 and a driven pulley 55, and the carriage 50 is reciprocally shifted along a guide rail 57 by driving the motor 53 in normal and reverse directions alternately. Incidentally, in order to apply a tension force to the timing belt 56, a support plate 58 for supporting the driven pulley 55 is pivotally mounted on a shaft 59 and the support plate 58 is biased by a tension spring 60 to apply a tension force to the belt 56.
With the above-mentioned arrangement for serially scanning the carriage, (1) when the total weight of the carriage 50 is increased (for example, when the number of the recording heads 51 mounted on the carriage is increased or when the capacity of the recording head is increased) and/or (2) when a shift stroke of the carriage 50 is increased (for example, when a size of the recording medium to be recorded or a size of an original to be read is great) and/or (3) when a scanning speed is increased, an output torque of the motor 53 is increased and the tension to the belt is also increased.
However, generally, if the output torque of the motor 53 is increased, the greater vibration of the belt 56 will occur, thus generating greater noise. Particularly, when a stepping motor is used as the drive motor, this phenomenon will be more noticeable. Further, as the weight of the carriage 50 is increased, when the carriage is rapidly accelerated from a stopped condition to a steady state or when the carriage is rapidly stopped from the steady state to the stopped condition, the shock vibration will occur, thus easily generating the noise. For these reasons, the increase in the mounting ability of the carriage 50 and the increase in the scanning speed were limited.